Not a whole lot of other planes flying around above 45,000 feet. Two to four minute naps were no danger. I'm sure he was well aware of every other aircraft above 40,000 feet anywhere within 2,000 miles.
Commercial flights don't typically go higher than FL410 (41,000 feet), I think, usually more like 35,000. Some of the high-end corporate jets like the Gulfstream V and Cessna Citation X are designed to be able to cruise all the way up to 51,000 feet, where they're most economical and less affected by weather. (Jet engines use less fuel at higher altitudes.)
}:-)4